import sys

import pygame
from bullet import Bullet
from alien import Alien

#def check_events():
#	"""响应按键和鼠标事件"""
#	for event in pygame.event.get():
#		if event.type == pygame.QUIT:
#			sys.exit()

def update_screen(ai_settings, screen, ship, aliens, bullets):
	"""更新屏幕上的图像，并切换到新屏幕"""
	#每次循环时重回屏幕
	screen.fill(ai_settings.bg_color)

	#在飞船和外星人后面重绘所有子弹
	for bullet in bullets.sprites():
		bullet.draw_bullet()

	ship.blitme()
	#aliens.blitme()
	aliens.draw(screen)	
	# 让最近绘制的屏幕可见
	pygame.display.flip()
	


def check_events(ai_settings, screen, ship, bullets):
	"""响应按键和鼠标事件"""
	for event in pygame.event.get():
		if event.type == pygame.QUIT:
			sys.exit()
		elif event.type == pygame.KEYDOWN:
			#check_keydown_events(event, ship)
			check_keydown_events(event, ai_settings, screen, ship, bullets)
		elif event.type == pygame.KEYUP:
			check_keyup_events(event, ship)


def check_keydown_events(event, ai_settings, screen, ship, bullets):
	"""响应按键"""
	if event.key == pygame.K_RIGHT:
		# 向右移动飞船
		ship.moving_right = True
	elif event.key == pygame.K_LEFT:
		ship.moving_left = True
	elif event.key == pygame.K_SPACE:
		# 创建一颗子弹，并将其加入到编组bullets中
		fire_bullet(ai_settings, screen, ship, bullets)
	elif event.key == pygame.K_q:
		sys.exit()

def check_keyup_events(event, ship):
	"""响应松开"""
	if event.key == pygame.K_RIGHT:
		ship.moving_right = False
	elif event.key == pygame.K_LEFT:
		ship.moving_left = False

def update_bullets(ai_settings, screen, ship, aliens, bullets):
	"""更新子弹的位置，并删除已消失的子弹"""
	#更新子弹的位置
	bullets.update()
	
	#删除已消失的子弹
	for bullet in bullets.copy():
		if bullet.rect.bottom <= 0:
			bullets.remove(bullet)

	check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets)

def check_bullet_alien_collisions(ai_settings, screen, ship, aliens, bullets):
	#检查是否有子弹击中外星人
	#如果是这样，就删除相应的子弹和外星人
	collisions = pygame.sprite.groupcollide(bullets, aliens, True, True)

	if len(aliens) == 0:
		#删除现有的子弹并重新建一群外星人
		bullets.empty()
		create_fleet(ai_settings, screen, ship, aliens)

def fire_bullet(ai_settings, screen, ship, bullets):
	"""如果没有达到限制，就发射一颗子弹"""
	#创建一个颗子弹，并将其加入到编组bullets中
	if len(bullets) < ai_settings.bullets_allowed:
		new_bullet = Bullet(ai_settings, screen, ship)
		bullets.add(new_bullet)

def get_number_aliens_x(ai_settings, alien_width):
	"""计算每行可以容纳多少个外星人"""
	available_space_x = ai_settings.screen_width - 2 * alien_width
	number_aliens_x = int(available_space_x / ( 2 * alien_width))
	return number_aliens_x

def get_number_rows(ai_settings, ship_height, alien_height):
	"""计算屏幕可以容纳多少行外星人"""
	available_space_y = (ai_settings.screen_height - (3 * alien_height ) - ship_height)
	number_rows = int( available_space_y / (2 * alien_height))
	return number_rows

def create_alien(ai_settings, screen, aliens, alien_number, row_number):
	"""创建一个外星人并将其放在当前行"""
	alien = Alien(ai_settings, screen)
	alien_width = alien.rect.width
	alien.x = alien_width + 2 * alien_width * alien_number
	alien.rect.x = alien.x
	alien.rect.y = alien.rect.height + 2 * alien.rect.height * row_number
	aliens.add(alien)

def create_fleet(ai_settings, screen, ship, aliens):
	"""创建外星人裙"""
	# 创建一个外星人，并计算一行克容纳多少个外星人
	# 外星人间距为外星人宽度
	alien = Alien(ai_settings, screen)
	number_aliens_x = get_number_aliens_x(ai_settings, alien.rect.width)
	number_rows = get_number_rows(ai_settings, ship.rect.height, alien.rect.height)	

	# 创建第一行外星人
	for row_number in range(number_rows):
		for alien_number in range(number_aliens_x):
			#创建一个外星人并将其加入当前行
			create_alien(ai_settings, screen, aliens, alien_number, row_number)


def update_aliens(ai_settings, aliens):
	"""更新外星人群中所有外星人的位置"""
	check_fleet_edges(ai_settings, aliens)
	aliens.update()

def check_fleet_edges(ai_settings, aliens):
	"""如果外星人到达边缘时采取相应的措施"""
	for alien in aliens.sprites():
		if alien.check_edges():
			change_fleet_direction(ai_settings, aliens)
			break

def change_fleet_direction(ai_settings, aliens):
	"""将整群外星人下移，并改变他们的方向"""
	for alien in aliens.sprites():
		alien.rect.y += ai_settings.fleet_drop_speed
	ai_settings.fleet_direction *= -1
	

